[gdal-dev] RFC 15: Band Masks vs #5621

[Even Rouault]

> 
> I am trying to help a developer how wants to use VRTs as an intermediary
> between a GeoRaster and a PNG, in order to produce thumbnails. In that
> case, does the VRT needs to describe the mask band so that the PNG's
> driver will received the filtered image, with the zeroes regions masked
> out?

You need to explicitely declare mask bands in the VRT. See the VRT 
documentation for that. But that will just declare the existence of the mask 
band, and will not do any processing such as zeroing masked regions.

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